1. Field of the Invention
The present invention concerns dielectric ceramics comprising CaZrO3 as a main ingredient and a multi-layer ceramic capacitor of excellent life characteristics using the same and, more in particular, it relates to dielectric ceramics used for a multi-layer ceramic capacitor including an internal electrode comprising Cu or Cu alloy and a multi-layer ceramic capacitor using the same.
2. Description of the Related Art
Heretofore, dielectric ceramics are used, for example, in dielectric resonators, filters, or multi-layer capacitors. For the dielectric ceramics used for the multi-layer capacitors, etc., it has been desired that the temperature coefficient of static capacitance (permittivity) is smaller along with increase in the working frequency of equipments in recent years (about 100 MHz to 2 GHz). Further, for the characteristics of the multi-layer capacitor used in high frequency circuits, it has been demanded that ESR (equivalent series resistance) is lower and the loss in the high frequency region is smaller (higher Q value). On the other hand, in view of reduction for the cost, it is necessary to select a base metal as an internal electrode of low specific resistivity. Accordingly, Cu is used instead of Ni and Pd. Further, for dielectrics, those having high Q value, small temperature coefficient of the permittivity and high reliability are demanded. Further, since Cu is used for the internal electrode, it has been demanded for the dielectrics that they can be fired at a relatively low temperature of 1080° C. or lower and they are non-reducing materials in order to prevent oxidation of Cu. Further, with an environmental view point, dielectrics not containing Pb or Bi are desired. Patent documents 1 and 2 disclose inventions concerning dielectric ceramic compositions satisfying such demands and further show the use of such dielectric ceramic compositions to multi-layer ceramic capacitors.
[Patent document 1] JP-A-5-217426
[Patent document 2] JP-A-11-106259
The patent document 1 shows a non-reducing dielectric ceramic composition containing (Ca1-xSrx)m(Zr1-yTiy)O3-zMnO2-wSiO2 as a main ingredient, and a(LiO1/2)—RO)-(1-a)(BO3/2—SiO2) (in which RO is at least one member of SrO, BaO and CaO) as an additive. The non-reducing dielectric ceramic composition “enables to obtain dielectric ceramics that can be fired at a low temperature of about 1000° C. or lower, can use copper as an electrode material, in addition, has a high Q value and permittivity, and is also stable for the temperature characteristic of the permittivity” (column [0005]). However, no sufficient study has been made on the improvement of the life characteristic of the multi-layer ceramic capacitor using Cu as the internal electrode.
The patent document 2 shows a dielectric ceramic composition containing a composite oxide represented by (CaO)x(Zr1-y.Tiy)O2, an Mn compound, and a glass ingredient represented by (aLi2O-bB2O3-cCaO). The dielectric ceramic composition “can be fired even in a reducing atmosphere at 1000° C. or lower, has high permittivity, in addition, is stable for the temperature characteristic of permittivity, has a Q value as Qf in a high frequency region (GHz band) of 10000 or more, with the Q value being remarkably improved particularly in the high frequency region” (column 0015). However, no sufficient study has been made on the improvement of the life characteristic of the multi-layer ceramic capacitor using Cu as the internal electrode.